Various different methods for the preparation of acrylsilanes are known. Thus, U.S. Pat. No. 3,258,477 discloses that acrylsilanes can be prepared by subjecting trialkoxysilanes to an addition reaction with allylacrylate or allylmethacrylate in the presence of platinum-containing catalysts. This method yields contaminated and discolored raw products which cannot be used for technical purposes as such. Especially acrylsilanes which are to be used for the manufacture of polymerizates require a high degree of purity and colorless appearance.
In order to separate acrylsilanes from the crude reaction mixtures, distillation, preferably under reduced pressure, is exclusively used. To avoid polymerization or gel formation during distillation, a number of stabilizers have been suggested, for example, p-benzoquinone, hydroquinone, 2.5-di-tert, butyl-beuzoquinone p-methoxyphenol or 2.5-di-tert.butyl-hydroquinone (see German Pat. No. 511 83 503 and 2,238,295 as well as European published application 0,162,390. However, when acrylsilanes are to be distilled, the stabilizing effect of the known stabilizers is either inadequate, or they cause the distillate to be discolored.
Additional stabilizers which have been proposed are N,N'-disubstituted p-phenylenediamines; such as N,N'-diphenyl-p-phenylenediamine, or sterically hindered phenols. These stabilizers, however, do not meet the requirements either which are expected of a good stabilizer. Thus, the use of substituted p-phenylenediamines causes polymerization in the sump to be substantially suppressed, but in the vapor phase the formation of "popcorn"-polymerizates occurs during distillation, which can lead to stoppages in the distillation columns, pipe systems or cooling system and can give rise to significant operational interruptions.
The use of substituted or sterically hindered phenols reduces the formation of "popcorn"-structures, but the formation of polymerizate in the sump is considerable unless very large amounts of these phenols are used. However, since these phenols pass over with the acrylsilanes during distillation, their proportion in the distillate is correspondingly high, which produces significant difficulties if these acrylsilanes are used for the preparation of polymerizates, because the phenols significantly inhibit or entirely suppress the polymerization.
European Pat. No. 0 247 501 discloses the preparation of acrylsilanes in the presence of phenolic stabilizers, aromatic amines or combinations of these. In this method, however, there is also the danger of gel formation.